FIG. 26 is a block diagram for explaining conventional laser equipment disclosed in “Highly efficient operation of diode laser transversely pumped high power Nd:YAG rod laser” by A. Takada et al., Advanced High-Power Lasers, Proceedings of SPIE, Vol. 3889.
In FIG. 26, 1a is a totally reflecting mirror with plane curvature, and 2a is a partially transmitting mirror with plane curvature. 5a, 5b, 5c and 5d, referred to as laser pumping sections hereinafter, are fundamental devices that singly or plurally constitute laser oscillators or laser amplifiers, and include respective laser active media 4a, 4b, 4c and 4d, and respective laser active medium pumping devices 3a, 3b, 3c and 3d, and as may be necessary, means for cooling them and for providing them with energizing power such as electric power. In FIG. 26, 111a is a reference mark indicating the beam-waist position on the end face of the totally reflecting mirror 1a; 111b is a reference mark indicating the beam-waist position between laser pumping sections 5a and 5b; 100a is a reference mark indicating the intermediate position in the excited portion of the laser active medium 4b; 111c is a reference mark indicating the beam-waist position on the end face of the partially transmitting mirror 2a; 111d is a reference mark indicating the beam-waist position between the laser pumping sections 5c and 5d; and 111e is a reference mark indicating the position of the beam waist formed on the beam-emitting side of the laser pumping section 5d. 
Moreover, 60a, 60b, 60c and 60d are reference marks indicating optical systems that include thermal lenses formed by the laser active media that are situated respectively between 111a and 111b, 111b and 111c, 111c and 111d, and 111d and 111e. A plurality of optical elements that are arranged along the laser beam axis is referred to as an optical system hereinafter, when it is shown as a whole.
The operation of the conventional example illustrated in FIG. 26 for the present invention is now described. A laser beam 7 generated in the laser oscillator that is constituted by the totally reflecting mirror 1a, the laser pumping sections 5a and 5b, and the partially transmitting mirror 2a passes through the partially transmitting mirror 2a and then is extracted from the oscillator and guided into the laser amplifier constituted by the laser pumping sections 5c and 5d, thus forming a laser beam 77 after being amplified in the course of passing through the laser amplifier. In this case, the laser pumping sections 5a, 5b, 5c and 5d are constituted by parts with the same specification and are excited by the same pumping energy.
The laser equipment constituted as shown in FIG. 26 is considered to be, as a whole, a cascade-type laser oscillator and amplifier wherein optical systems 60a each acting as a fundamental unit are arranged periodically in series, because the optical systems 60b, 60c and 60d are identical to the optical system 60a, provided that only beam mode shape inside the oscillator and amplifier, and essential factors—focusing elements and propagation distances—which significantly affect the beam mode shape are thought, without taking into account optical properties such as gain, the totally reflecting mirror and the totally transmitting mirror. For this reason, as described thereinafter, the beam diameter in the position 111e significantly varies depending on changes in the pumping energy.
In a conventional cascade-type solid-state laser oscillator and amplifier as described above, the diameter of the beam in places in which the wavelength-conversion active media are positioned varies depending on the pumping intensity, and the condition of the wavelength conversion accordingly changes depending on the pumping intensity when wavelength conversion using the extracted beam is carried out, since emitted laser beam diameter and beam wavefront curvature varies significantly depending on the pumping intensity. Moreover, when a laser beam generated in the conventional laser equipment is guided into an optical fiber, the light-guiding conditions depends largely on the laser pumping intensity, since the diameter of the emitted beam and the wavefront curvature varies significantly depending on the pumping intensity. In addition, when a laser beam extracted from the conventional laser equipment is used for machining work, the processing conditions varies depending on the pumping intensity of the laser equipment, e.g., laser beam energy, since emitted beam varies depending on the pumping intensity.
On the other hand, assuming for example that the amplifier portion consisting of the laser pumping sections 5c and 5d shown in FIG. 26 are independently used as an amplifier and would receive an incident beam through the position 111c, since the position 111c is, from the viewpoint of designing the cascade-type amplifier, the one whereat the beam diameter varies, the beam parameters for the incident beam would need to be changed in accordance with the pumping intensity. Furthermore, when attempting to configure variable-output laser equipment utilizing an incident beam with a constant beam diameter and beam wavefront curvature, and varying the pumping intensity of the amplifier, since the beam behavior in the amplifier would not be that of a cascade type having a periodic structure, there have been problems such as that the design of the amplifier has been complicated, that multiplication of amplification stages has been difficult, and that the volume where the amplified beam mode and the excited region overlap has lessened, hindering high-efficiency amplification.
The present invention has been made to address the foregoing problems of the conventional laser equipment; it is an object of the present invention to provide laser equipment wherein the beam diameter of an emitted laser beam and the wavefront curvature have reduced dependence on the pumping intensity, as well as laser equipment that can efficiently amplify an incident beam having fixed beam parameters.